Investigation of energetic surface state distributions at real surfaces of silicon after treatment with HF and H₂O using large-signal photovoltage pulses

Abstract

It is shown that the field-modulated large-signal photovoltage offers definite methodological advantages in comparison to other methods more frequently used for the determination of surface state distribution. Apparatus and sample preparations are described. The distribution of fast states in the forbidden gap at real silicon surfaces was studied after treatment in HF and rinsing in H2O up to times in excess of 100 h. Whilst for short rinsing times minimum concentrations of 3*1012 states cm-2 eV-1 were found, prolonged rinsing led to an 'intrinsic' distribution where the concentration in the minimum was lower by a factor of ten. The results are compared with those recently obtained at thermally oxidised silicon. A meaningful separation of surface states into three groups of different physical origin is possible both for real and for oxidised silicon surfaces. Fluoridation as a probable cause of extrinsic surface states, model descriptions of intrinsic states and, finally, certain aspects concerning semiconductor device technology are discussed.

Surface photovoltage phenomena: theory, experiment, and applications

“…78 are generally consistent with other investigations of Flietner et al [717,718,720,721,723], as well as with the earlier analyses of Allen and Gobeli [710], Yamagishi [572], and Lam [716]. All of these show that well-passivated Si surfaces feature a`U-shaped' distribution of surface states, which is typically symmetric about midgap.…”

“…In all cases, reasonable agreement with ac conductance data (where that method was applicable) was obtained. Consequently, Flietner, Heilig, et al extended the ®eld modulation approach to the study of free Si surfaces and non-metallized Si/insulator interfaces by employing an`arti®cial' MIS structure (i.e., a contactless gate electrode ± see Section 3.2) in conjunction with SPV-based V 0 s -determining methods discussed in Section 5.2.2 [717]. For example, the analysis based on Eq.…”

“…For example, the analysis based on Eq. (5.34) has been applied to the study of HF and H 2 O treated Si(111) surfaces [717,718], Si(111)/lead-boro-alumino-silicate glass [713] and Si/porous Si [719], and mostly chemically [720±725] and electrochemically [714,726,727] Hterminated Si (111) surfaces. The same approach was used by Venger et al to study the surface state distribution at real Ge [568] and GaAs [569] surfaces.…”

“…This immediately explains why most successful investigations described so far were limited to unpinned Si surfaces. In addition, possible hysteresis effects due to capture of charge in surface states must be taken into account when performing measurements as a function of gate bias [568,712,717]. If the bulk state density is very high, Q sc (and hence Q ss ) can no longer be calculated from Eq.…”

Analysis of Charge Versus the Surface Fermi Level Position at Silicon Surface

“…The abrupt change in Qsc near the midgap points at the existence of another group of surface states, maybe of an impurity character [7].…”